"I am in deep shock-I have lost a beloved friend-the kindest, most generous soul and a brilliant artist. RIP @GeorgeMichael," he captioned a photo of the two together.

The two were friends for a number of decades, and also collaborated on this hit "Don't Let The Sun Go Down on Me," in 1991, a duet re-release of John's former solo song from the 70s.

John wasn't the only friend of Michael's to pay tribute to him on social media after his death, with his former bandmate Andrew Ridgeley also reaching out to share his sadness as well.

Heartbroken at the loss of my beloved friend Yog. Me, his loved ones, his friends, the world of music, the world at large. 4ever loved. A xx https://t.co/OlGTm4D9O6 — Andrew Ridgeley (@ajridgeley) December 26, 2016

"Heartbroken at the loss of my beloved friend Yog. Me, his loved ones, his friends, the world of music, the world at large. 4ever loved. Xx," he wrote in one post.

He also later shared a second post honoring his friend after the BBC tweeted a quote by Michael, where he said "I still believe that music is one of the greatest gifts that God gave to man."

"God didn't give it, you did old friend. Cleft with grief. A xx," Ridgeley wrote. As Wham! Ridgeley and Michael were best known for 80s pop hits like "Wake Me Up Before You Go-Go," "Careless Whisper," and "Freedom." The two officially broke up in 1986, but not before releasing a farewell song together, "The Edge of Heaven."

No immediate cause of death was given for Michael, though some reports indicate his manager has claimed it was heart failure.

Michael's death is also the latest in a year full of hard-hitting celebrity deaths. Earlier in the year, fellow musicians Prince, David Bowie, Glenn Frey and Merle Haggard all passed away, as have several other entertainers and athletes, including Alan Rickman, Doris Roberts, Gene Wilder, Anton Yelchin, Florence Henderson, Alan Thicke, Garry Marshall and Muhammad Ali.